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        <td class="header">Orthorectification</td>
        <td class="header" align="right"><a href="../general/Overview.html"><img src="../images/snap_header.jpg" border="0"></a></td>
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<h3>SAR Simulation Terrain Correction Operator</h3>

<p>The operator generates orthorectified image using rigorous SAR simulation.</p>

<h4>Major Processing Steps</h4>

<p>Some major steps of the procedure are listed below:</p>
<ol>
    <li><span style="font-weight: bold;">SAR simulation:</span> Generate simulated SAR image using DEM, the geocoding
        and orbit state
        vectors from the original SAR image, and mathematical modeling of SAR imaging geometry.
        The simulated SAR image will have the same dimension and resolution as the original image.
        For detailed steps and parameters used in SAR simulation, please refer to the <a href="SARSimulationOp.html">SAR
            Simulation Operator</a>.
    </li>

    <li><span style="font-weight: bold;">Co-registration:</span> The simulated SAR image (master) and the original SAR
        image (slave)
        are co-registered and a WARP function is produced. The WARP function maps each pixel in the
        simulated SAR image to its corresponding position in the original SAR image. For detailed
        steps and parameters used in co-registration, please refer to the&nbsp;<a href="GCPSelectionOp.html">GCP
            Selection Operator</a>.
    </li>

    <li><span style="font-weight: bold;">Terrain correction:</span> Traverse DEM grid that covers the imaging area. For
        each cell in
        the DEM grid, compute its corresponding pixel position in the simulated SAR image using
        SAR model. Then its corresponding pixel position in the original SAR image can be found
        with the help of the WARP function. Finally the pixel value for the
        orthorectified image can be obtained from the original SAR image using&nbsp;interpolation.
    </li>
</ol>
<h4>Products Supported</h4>
<ul>
    <li>ASAR (IMS, IMP, IMM, APP, APM, WSM),&nbsp;ERS products (SLC, IMP),&nbsp;RADARSAT-2, TerraSAR-X are fully
        supported.
    </li>
    <li>Some third party missions are not fully supported.
    </li>
</ul>
<h4>DEM Supported</h4>

<p>Currently, only the DEMs with geographic coordinates (P<sub>lat</sub>, P<sub>lon</sub>, P<sub>h</sub>) referred to
    global geodetic ellipsoid reference WGS84 (and height in meters) are properly supported.</p>

<p>Various different types of Digital Elevation
    models can be used (ACE, GETASSE30,&nbsp;ASTER, SRTM 3Sec&nbsp;GeoTiff).</p><p>The STRM v.4 (3&#8221; tiles) from the Joint Research Center
    FTP (xftp.jrc.it) will automatically be downloaded in tiles for&nbsp; the area covered by the image to be
    orthorectified. The tiles will be downloaded to the folder .snap\AuxData\DEMs\SRTM_DEM\tiff.</p>



<p>Please
    note that for ACE and SRTM, the height information (being referred to
    geoid EGM96) is automatically corrected to obtain height relative to
    the WGS84 ellipsoid. For Aster Dem height correction is not yet
    applied. </p>

<p>Note also that the SRTM DEM covers area between -60
    and 60 degrees latitude. Therefore, for orthorectification of product
    of high latitude area, different DEM should be used. </p>

<p>User can also use external DEM file in Geotiff format which, as specified above, must be with geographic coordinates&nbsp;(P<sub>lat</sub>,
    P<sub>lon</sub>, P<sub>h</sub>) referred to global geodetic ellipsoid reference WGS84 (and height in meters).</p>

<p>Note that the same DEM is used by both SAR simulation and Terrain correction. The DEM is selected through SAR
    Simulation UI.</p><h4>Pixel Spacing</h4>

<p>Besides
    the default suggested pixel spacing computed with parameters in the
    metadata, user can specify output pixel spacing for the orthorectified
    image.</p>

<p> The
    pixel spacing can be entered in both meters and degrees. If the pixel
    spacing in one unit is entered, then &nbsp;the pixel spacing in another
    unit is computed
    automatically.</p>

<p> The calculations of the pixel spacing in meters and in
    degrees&nbsp;are given by the following equations:&nbsp;<span style="font-size: 11pt; font-family: &quot;Times New Roman&quot;;" lang="EN-GB"></span><i><span style="font-size: 12pt; font-family: &quot;Times New Roman&quot;;" lang="EN-GB"></span></i><span style="font-size: 7pt; font-family: Symbol;" lang="EN-GB"></span><i><span style="font-size: 12pt; font-family: &quot;Times New Roman&quot;;" lang="EN-GB"></span></i><span style="font-size: 7pt; font-family: Symbol;" lang="EN-GB"></span><i><span style="font-size: 12pt; font-family: &quot;Times New Roman&quot;;" lang="EN-GB"></span><span style="font-size: 8pt; font-family: &quot;Times New Roman&quot;;" lang="EN-GB"></span></i><span style="font-size: 12pt; font-family: &quot;Times New Roman&quot;;" lang="EN-GB"></span></p>

<p style="margin-left: 40px;">pixelSpacingInDegree = pixelSpacingInMeter / EquatorialEarthRadius * 180 / PI;</p>

<p style="margin-left: 40px;">pixelSpacingInMeter = pixelSpacingInDegree * PolarEarthRadius&nbsp; * PI / 180;</p>

<p>where&nbsp;EquatorialEarthRadius = 6378137.0 m and PolarEarthRadius = 6356752.314245 m as given in WGS84.&nbsp;</p><h4>Radiometric Normalization</h4>

<p>This option implements a radiometric normalization based on the approach proposed by Kellndorfer et al., TGRS, Sept.
    1998 where <br><img style="width: 233px; height: 67px;" alt="" src="images/range_doppler_eq5.jpg"></p>

<p>In current implementation <span style="font-style: italic;">&#952;</span><sub style="font-style: italic;">DEM</sub>
    is the local incidence angle projected into the range plane and defined
    as the angle between the incoming radiation vector and the projected
    surface normal vector into range plane[2]. The range plane is the plane
    formed by the satellite position, backscattering element position and
    the earth centre.&nbsp;</p>

<p>Note that among&nbsp;<span style="font-style: italic;">&#963;</span><sup style="font-style: italic;"><sub>0</sub></sup>, <span style="font-style: italic;">&#947;</span><sup style="font-style: italic;"><sub>0</sub></sup> and <span style="font-style: italic;">&#946;</span><sup style="font-style: italic;"><sub>0</sub></sup> bands output in the target product, only&nbsp;<span style="font-style: italic;">&#963;</span><sup style="font-style: italic;"><sub>0</sub></sup> is real band while
    <span style="font-style: italic;">&#947;</span><sup style="font-style: italic;"><sub>0</sub></sup> and <span style="font-style: italic;">&#946;</span><sup style="font-style: italic;"><sub>0</sub></sup> are virtual
    bands expressed in terms of <span style="font-style: italic;">&#963;</span><sup style="font-style: italic;"><sub>0</sub></sup>&nbsp;and incidence angle. Therefore, <span style="font-style: italic;">&#963;</span><sup style="font-style: italic;"><sub>0</sub></sup>&nbsp;and
    incidence angle are automatically saved and output if <span style="font-style: italic;">&#947;</span><sup style="font-style: italic;"><sub>0</sub></sup> or <span style="font-style: italic;">&#946;</span><sup style="font-style: italic;"><sub>0</sub></sup> is selected.</p>

<p>For <span style="font-style: italic;">&#963;</span><sup style="font-style: italic;"><sub>0</sub></sup> and <span style="font-style: italic;">&#947;</span><sup style="font-style: italic;"><sub>0</sub></sup>&nbsp;calculation,
    by default the projected local incidence angle from DEM [2] (local
    incidence angle projected into range plane) option is selected, but the
    option of incidence angle from ellipsoid correction (incidence angle
    from tie points of the source product) is also available.<br></p><h4>ENVISAT ASAR</h4>

<p>
    The correction factors [3] applied to the original image depend on if
    the product is complex or detected and&nbsp;the selection of Auxiliary
    file (ASAR XCA file).&nbsp;</p><h4>Complex Product (IMS, APS)</h4>
<ul>
    <li><span style="font-weight: bold;">Latest AUX File</span>&nbsp;(&amp; use projected local incidence angle computed
        from DEM):<p>&nbsp;The
            most recent ASAR XCA available from C:\Program
            Files\NEST4A\auxdata\envisat compatible with product date is
            automatically selected. According to this XCA file, calibration
            constant, range spreading loss and antenna pattern gain are obtained.</p></li>
    <ul>
        <li><span style="text-decoration: underline;">Applied factors</span>:</li>
    </ul>
    <ul>
        <ol>
            <li><p>apply projected local incidence angle into the range plane correction</p></li>
            <li><p>apply calibration constant correction based on the XCA file<br></p></li>
            <li><p>apply range spreading loss correction based on the XCA file and DEM geometry<br></p></li>
            <li><p>apply antenna pattern gain correction based on the XCA file and DEM geometry<br></p></li>
        </ol>
    </ul>
    <li><span style="font-weight: bold;">External AUX File</span>&nbsp;(&amp; use projected local incidence angle
        computed from DEM):<p>&nbsp;User
            can select a specific ASAR XCA file available from C:\Program
            Files\NEST4A\auxdata\envisat or from another repository. According to
            this selected XCA file, calibration constant, range spreading loss and
            antenna pattern gain are computed.</p></li>
    <ul>
        <li><span style="text-decoration: underline;">Applied factors</span>:</li>
    </ul>
    <ul>
        <ol>
            <li><p>apply projected local incidence angle into the range plane correction</p></li>
            <li><p>apply calibration constant correction based on the selected XCA file<br></p></li>
            <li><p>apply range spreading loss correction based on the selected XCA file and DEM geometry<br></p></li>
            <li><p>apply antenna pattern gain correction based on the selected XCA file and DEM geometry<br></p></li>
        </ol>
    </ul>
</ul>
<h4>Detected Product (IMP, IMM, APP, APM, WSM)</h4>
<ul>
    <li><span style="font-weight: bold;">Latest AUX File</span>&nbsp;(&amp; use projected local incidence angle computed
        from DEM):<p>The
            most recent ASAR XCA available from C:\Program
            Files\NEST4A\auxdata\envisat compatible with product date is
            automatically selected. Basically with this option all the correction
            factors applied to the original SAR image based on product XCA file
            used during the focusing, such as antenna pattern gain and range
            spreading loss, are removed first. Then new factors computed according
            to the new ASAR XCA file together with calibration constant and local
            incidence angle correction factors are applied during the radiometric
            normalisation process.</p></li>
    <ul>
        <li><span style="text-decoration: underline;">Applied factors</span>:</li>
    </ul>
    <ul>
        <ol>
            <li><p>remove antenna pattern gain correction based on product XCA file</p></li>
            <li><p>remove range spreading loss correction based on product XCA file<br></p></li>
            <li><p>apply projected local incidence angle into the range plane correction<br></p></li>
            <li><p>apply calibration constant correction based on new XCA file</p></li>
            <li><p>apply range spreading loss correction based on new XCA file and DEM geometry</p></li>
            <li><p>apply new antenna pattern gain correction based on new XCA file and DEM geometry<br></p></li>
        </ol>
    </ul>
    <li><span style="font-weight: bold;">Product AUX File</span>&nbsp;(&amp; use projected local incidence angle
        computed from DEM):<p>&nbsp;The
            product ASAR XCA file employed during the focusing is used. With this
            option the antenna pattern gain and range spreading loss are kept from
            the original product and only the calibration constant and local
            incidence angle correction factors are applied during the radiometric
            normalisation process.</p></li>
    <ul>
        <li><span style="text-decoration: underline;">Applied factors</span>:</li>
    </ul>
    <ul>
        <ol>
            <li><p>apply projected local incidence angle into the range plane correction</p></li>
            <li><p>apply calibration constant correction based on product XCA file<br></p></li>
        </ol>
    </ul>
</ul>
<ul>
    <li><span style="font-weight: bold;">External AUX File</span>&nbsp;(&amp; use projected local incidence angle
        computed from DEM):<p>&nbsp;User
            can select a specific ASAR XCA file available from&nbsp;the installation folder or from another repository.
            Basically with
            this option all the correction factors applied to the original SAR
            image based on product XCA file used during the focusing, such as
            antenna pattern gain and range spreading loss, are removed first. Then
            new factors computed according to the new selected ASAR XCA file
            together with calibration constant and local incidence angle correction
            factors are applied during the radiometric normalisation process.</p></li>
    <ul>
        <li><span style="text-decoration: underline;">Applied factors</span>:</li>
    </ul>
    <ul>
        <ol>
            <li><p>remove antenna pattern gain correction based on product XCA file</p></li>
            <li><p>remove range spreading loss correction based on product XCA file<br></p></li>
            <li><p>apply projected local incidence angle into the range plane correction<br></p></li>
            <li><p>apply calibration constant correction based on new selected XCA file</p></li>
            <li><p>apply range spreading loss correction based on new selected XCA file and DEM geometry</p></li>
            <li><p>apply new antenna pattern gain correction based on new selected XCA file and DEM geometry<br></p>
            </li>
        </ol>
    </ul>
</ul>
<p>
    Please note that if the product has been previously multilooked then
    the radiometric normalization does not correct the antenna pattern and
    range spreading loss and only constant and incidence angle corrections
    are applied. This is because the original antenna pattern and the range
    spreading loss correction cannot be properly removed due to the pixel
    averaging by multilooking. <br></p>

<p>If
    user needs to apply a radiometric normalization, multilook and terrain
    correction to a product, then user graph
    &#8220;RemoveAntPat_Multilook_Orthorectify&#8221; could be used.<br></p><h4>ERS 1&amp;2</h4>

<p>For ERS 1&amp;2 the radiometric normalization cannot be applied directly to original ERS product.<br></p>

<p>Because
    of the Analogue to Digital Converter (ADC) power loss correction , a
    step before is required to properly handle the data. It is necessary to
    employ the Remove Antenna Pattern Operator which performs the following
    operations:</p>

<p>&nbsp;For Single look complex (SLC, IMS) products<br></p>
<ul>
    <li>apply ADC correction</li>
</ul>
<p>For Ground range (PRI, IMP) products:</p>
<ul>
    <li>remove antenna pattern gain</li>
    <li>remove range spreading loss</li>
    <li>apply ADC correction<span style="font-weight: bold;"></span></li>
</ul>
<p>After
    having applied the Remove Antenna Pattern Operator to ERS data, the
    radiometric normalisation can be performed during the Terrain
    Correction.<br></p>

<p>The applied factors in case of "USE projected angle from the DEM" selection are:<br></p>
<ol>
    <li>apply projected local incidence angle into the range plane correction</li>
    <li>apply absolute calibration constant correction</li>
    <li>apply range spreading loss correction based on product metadata and DEM geometry</li>
    <li>apply new antenna pattern gain correction based on product metadata and DEM geometry</li>
</ol>
<p>To apply radiometric normalization and terrain correction for ERS, user can also use one of the following user
    graphs:<br></p>
<ul>
    <li>RemoveAntPat_Orthorectify</li>
    <li>RemoveAntPat_Multilook_Orthorectify</li>
</ul>
<h4>RADARSAT-2</h4>
<ul>
    <li>In
        case of "USE projected angle from the DEM" selection, the radiometric
        normalisation is performed applying the product LUTs and multiplying by
        (sin &#61553;DEM/sin &#61553;el), where &#61553;DEM is projected local incidence angle into
        the range plane and &#61553;el is the incidence angle computed from the tie
        point grid respect to ellipsoid.
    </li>
    <li>In case of selection of "USE
        incidence angle from Ellipsoid", the radiometric normalisation is
        performed applying the product LUT.
    </li>
</ul>
<p>These LUTs allow one to
    convert the digital numbers found in the output product to
    sigma-nought, beta-nought, or gamma-nought values (depending on which
    LUT is used).<br></p><h4>TerraSAR-X</h4>
<ul>
    <li>In case of "USE projected angle from the DEM" selection, the radiometric normalisation is performed applying<br>
        <ol>
            <li>projected local incidence angle into the range plane correction</li>
            <li>absolute calibration constant correction</li>
        </ol>
    </li>
    <li>In case of " USE incidence angle from Ellipsoid " selection, the radiometric normalisation is performed applying<br>
        <ol>
            <li>projected local incidence angle into the range plane correction</li>
            <li>absolute calibration constant correction</li>
        </ol>
    </li>
</ul>
Please note that the simplified approach&nbsp; where Noise Equivalent Beta Naught is neglected has been implemented.<br>
<h4>Cosmo-SkyMed</h4>
<ul>
    <li>In case of "USE projected angle from the DEM" selection, the radiometric normalisation is performed deriving
        <span style="font-style: italic;">&#963;</span><sup style="font-style: italic;"><sub>0</sub></sup><sub style="font-style: italic;">Ellipsoid</sub> [7] and then multiplying by (sin<span style="font-style: italic;">&#952;</span><sub style="font-style: italic;">DEM</sub> /&nbsp;sin<span style="font-style: italic;">&#952;</span><sub style="font-style: italic;">el</sub>), where <span style="font-style: italic;">&#952;</span><sub style="font-style: italic;">DEM</sub>&nbsp;is the
        projected local incidence angle into the range plane and <span style="font-style: italic;">&#952;</span><sub style="font-style: italic;">el</sub>&nbsp;is the incidence angle computed from the tie point grid
        respect to ellipsoid.
    </li>
    <li>In case of selection of "USE incidence angle from Ellipsoid", the radiometric normalisation is performed
        deriving <span style="font-style: italic;">&#963;</span><sup style="font-style: italic;"><sub>0</sub></sup><sub style="font-style: italic;">Ellipsoid</sub> [7] <br></li>
</ul>
<span style="text-decoration: underline; font-weight: bold;">Definitions:</span><br>
<ol>
    <li>The
        local incidence angle is defined as the angle between the normal vector
        of the backscattering element (i.e. vector perpendicular to the ground
        surface) and the incoming radiation vector (i.e. vector formed by the
        satellite position and the backscattering element position) [2].
    </li>
    <li>The
        projected local incidence angle from DEM is defined as the angle
        between the incoming radiation vector (as defined above) and the
        projected surface normal vector into range plane. Here range plane is
        the plane formed by the satellite position, backscattering element
        position and the earth centre [2].<br></li>
</ol>
<h4>Layover-Shadow Mask Generation</h4>

<p>This
    operator can also generate layover-shadow mask for the orthorectified
    image. The layover effect is caused by the fact that the signal
    backscattered from the top of the mountain is actually received earlier
    than the signal from the bottom, i.e. the fore slope is reversed. The
    shadow effect is caused by the fact that no information is received
    from the back slope. &nbsp;This operator generates the layover-shadow
    mask as a separate band using the 2-pass algorithm given in section 7.4
    in [2]. The value coding for the layover-shadow mask is defined as the
    follows:</p>
<ul>
    <li>0 - corresponding image pixel is not in layover, nor shadow&nbsp;</li>
    <li>1 - corresponding image pixel is in layover</li>
    <li>2 - corresponding image pixel is in shadow&nbsp;</li>
    <li>3 - corresponding image pixel is in layover and shadow</li>
</ul>
<p>User
    can select&nbsp;output&nbsp;the layover-shadow mask by checkmarking
    "Save Layove-Shadow Mask as band" box in SAR-Simulation tab.</p>

<p>To
    visualize the layover-shadow mask, user can bring up the orthorectified
    image first, then go to layer manager and add the layover-shadow mask
    band as a layer.</p><h4>Parameters Used</h4>&nbsp; &nbsp;The following parameters are used by the Terrain Correction
step:
<ol>
    <li>RMS Threshold: The criterion for eliminating invalid GCPs. (see Help for
        <a href="WarpOp.html">Warp Operator</a> for detail)
    </li>
    <li>WARP Polynomial Order: The degree of the WARP polynomial. The valid values are
        1, 2 and 3. (see Help for <a href="WarpOp.html">Warp Operator</a> for detail)
    </li>
    <li>DEM Resampling Method: Interpolation method for obtaining elevation values
        from the original DEM file. The following interpolation methods are available:
        nearest neighbour, bi-linear, cubic convolution, bi-sinc and bi-cubic interpolations.
    </li>
    <li>Image Resampling Method: Interpolation methods for obtaining pixel values
        from the source image. Three interpolation methods are available:
        nearest neighbour, bi-linear, cubic and bi-sinc interpolations.
    </li>
    <li>Pixel Spacing (m): User can specify pixel spacing&nbsp;in meters for orthorectified image. If
        no pixel spacing is specified,&nbsp;then default&nbsp;pixel spacing
        computed from the source SAR image is used. For details, the reader is referred to <span style="font-weight: bold;">Pixel Spacing</span> section above.
    </li>
    <li>Pixel Spacing (deg): User
        can also specify the pixel spacing&nbsp;in degrees. &nbsp;If the value
        of any of the two pixel spacing is changed, the other one is updated
        automatically.&nbsp;For details, the reader is referred to <span style="font-weight: bold;">Pixel Spacing</span>
        section above.
    </li>
    <li>Save DEM as band: Checkbox indicating that DEM will be save as a band in the
        target product.
    </li>
    <li>Save local incidence angle as band: Checkbox indicating that local incidence
        angle will be save as a band in the target product.
    </li>
    <li>Save projected local incidence angle as band: Checkbox indicating that the
        projected local incidence angle will be save as a band in the target product.
    </li>
    <li>Save selected source band: Checkbox indicating that orthorectified
        images of user selected bands will be saved without applying
        radiometric normalization.
    </li>
    <li>Apply radiometric normalization: Checkbox indicating that radiometric normalization will be applied to the
        orthorectified image.
    </li>
    <li>Save Sigma0 as a band: Checkbox indicating that sigma0 will be
        saved as a band in the target product. The Sigma0 can be generated
        using projected local incidence angle, local incidence angle or incidence angle from
        ellipsoid.
    </li>
    <li>Save
        Gamma0 as a band: Checkbox indicating that Gamma0 will be saved as a
        band in the target product. The Gamma0 can be generated using projected
        local incidence angle, local incidence angle or incidence angle from ellipsoid.
    </li>
    <li>Save Beta0 as a band: Checkbox indicating that Beta0 will be saved as a band in the target product.</li>
    <li>Auxiliary
        File:&nbsp;available only for ASAR. User selected ASAR XCA file for radiometric normalization. The
        following options are available: <span style="font-weight: bold;">Latest Auxiliary File</span>, <span style="font-weight: bold;">Product
Auxiliary
File</span> (for detected product only) and <span style="font-weight: bold;">External Auxiliary File</span>. By
        default,&nbsp;the Latest Auxiliary
        File&nbsp;is used. Details about the corrections applied according to the XCA selection are provided in <span style="font-weight: bold;">Radiometric Normalisation</span> &#8211; Envisat ASAR section above.
    </li>
    <li>Show
        Range and Azimuth Shifts: Checkbox indicating that range and azimuth
        shifts (in m) for all valid GCPs will be displayed. The row and column
        shifts of each slave GCP away from its initial position are output to a
        text file.
    </li>
</ol>
<br>

<p><img style="width: 600px; height: 560px;" alt="" src="images/sar_sim_terrain_corr_dlg.jpg"><br></p>

<p>&nbsp;Figure 1. SAR Sim Terrain Correction dialog box</p><h4>Detailed&nbsp;Algorithm for Layover-Shadow Mask
    Generation</h4>
<ol>
    <li>First&nbsp;a DEM image is created by the SAR Simulation operator using the geocoding of the original SAR image.
        The DEM
        image has the same dimension as the original SAR image with each pixel value of the DEM image is the
        elevation of the corresponding pixel in the original SAR image.&nbsp;</li>
    <li>Then&nbsp;2-pass
        method (see section 7.4 in [2]) is applied to each range line in the
        DEM image to
        generate the layover and shadow mask for the DEM image. The 2-pass
        method compares the slant range for a DEM cell to&nbsp;slant ranges of
        other cells in the same range line to determine if the DEM cell will be
        imaged in layover or shadow area.
    </li>
    <li>Next the layover-shadow mask for the DEM image is mapped&nbsp;to the simulated image&nbsp;to create the mask
        for the simulated image. The map is done using SAR simulation.
    </li>
    <li>The layover-shadow mask for the simulated SAR
        image is then mapped to the original SAR image using the WARP function, which&nbsp;was
        created during co-registration of the simulated SAR image and the
        original SAR image.
    </li>
    <li>Finally the mask for the original SAR image
        is mapped to the orthorectified image domain to produce the mask for
        the orthorectified image.
    </li>
</ol>
&nbsp;&nbsp;&nbsp; The algorithm is summarized in the figure below.<p><img style="width: 637px; height: 491px;" alt="" src="images/layover_shadow_mask.jpg"></p>

<p>&nbsp;Figure 2. Layover-shadow mask generation</p>

<p></p>

<p><i ,j="">Reference:</i></p>

<p>[1] Small D., Schubert A.,
    Guide to ASAR Geocoding, RSL-ASAR-GC-AD, Issue 1.0, March 2008</p>

<p>[2]&nbsp;Schreier G., <span style="font-style: italic;">SAR geocoding: data and systems</span>, Wichmann-Verlag,
    Karlsruhe, Germany, 1993</p>

<p>[3] Rosich B., Meadows P., Absolute calibration of ASAR Level 1 products,
    ESA/ESRIN, ENVI-CLVL-EOPG-TN-03-0010, Issue 1, Rev. 5, October 2004</p>

<p>[4]
    Laur H., Bally P., Meadows P., S�nchez J., Sch�ttler B., Lopinto E.
    &amp; Esteban D., ERS SAR Calibration: Derivation of &#963;0 in ESA ERS SAR
    PRI Products, ESA/ESRIN, ES-TN-RS-PM-HL09, Issue 2, Rev. 5f, November
    2004&nbsp;</p>

<p>[5] RADARSAT-2 PRODUCT FORMAT DEFINITION - RN-RP-51-2713 Issue 1/7: March 14, 2008</p>

<p>[6] Radiometric Calibration of TerraSAR-X data - TSXX-ITD-TN-0049-radiometric_calculations_I1.00.doc, 2008</p>

<p>[7] For further details about Cosmo-SkyMed calibration please contact Cosmo-SkyMed Help Desk at&nbsp;<font color="black" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;" lang="EN-GB"><a href="mailto:info.cosmo@e-geos.it" moz-do-not-send="true">info.cosmo@e-geos.it</a></span></font></p>

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